Building custom kernel in NixOS

custom-kernel.nix

{ pkgs, ... }:

# Modified version of pkgs.linuxPackages_custom to accept kernelPatches
let
  customPackage = { version, src, configfile, modDirVersion ? pkgs.lib.versions.pad 3 version, kernelPatches ? [ ], allowImportFromDerivation ? true }:
    pkgs.lib.recurseIntoAttrs (pkgs.linuxPackagesFor (pkgs.linuxManualConfig {
      inherit version src configfile modDirVersion kernelPatches allowImportFromDerivation;
    }));

in
customPackage {
  version = "6.10.0-rc3-bcache";
  modDirVersion = "6.10.0-rc3";
  configfile = ./config_6_10_rc3;
  src = pkgs.fetchurl {
    url = "https://git.kernel.org/torvalds/t/linux-6.10-rc3.tar.gz";
    hash = "sha256-z5Z89iBz9YojSC3RpXlEPjqXhXCt1AIxqlK7DL9lnkg=";
  };
  kernelPatches = [{
    name = "bcachefs";
    patch = ./bcachefs.patch;
  }];
}

hardware-configuration.nix

{
  ...
  boot.initrd.includeDefaultModules = false; #Optional if you don't want all the default modules
  boot.kernelPackages = import ./custom-kernel.nix { inherit pkgs; };
  ...
}